Gas turbine engine airfoil mistuning

ABSTRACT

A circumferential airfoil array that provides a total airfoil count for the stage and that includes first and second sets of airfoils with different vibrational frequencies. First and second arcuate regions are arranged opposite one another and third and fourth arcuate regions are arranged opposite one another. The first set of airfoils has first primary, first secondary and first tertiary airfoil groups. The second set of airfoils has second primary, second secondary and second tertiary airfoil groups. The first primary airfoil group and second primary airfoil group are respectively arranged in the first and second arcuate regions. The first secondary airfoil group and second secondary airfoil group are arranged in the third arcuate region. The first tertiary airfoil group and the second tertiary airfoil group are arranged in the fourth arcuate region. The first and second arcuate regions provide greater than 50% of the total airfoil count.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.62/058,297, which was filed on Oct. 1, 2014 and is incorporated hereinby reference.

BACKGROUND

This disclosure relates to an airfoil array for a gas turbine engine.

A gas turbine engine typically includes a fan section, a compressorsection, a combustor section and a turbine section. Air entering thecompressor section is compressed and delivered into the combustorsection where it is mixed with fuel and ignited to generate a high-speedexhaust gas flow. The high-speed exhaust gas flow expands through theturbine section to drive the compressor and the fan section. Thecompressor section typically includes low and high pressure compressors,and the turbine section includes low and high pressure turbines.

The compressor and turbine section includes circumferential arrangementsof fixed and rotating stages. Structural vibratory coupling betweenadjacent airfoils can occur during engine operation. For rotating stagesof the engine, blade mistuning has been used in which there are two setsof blades are arranged in circumferentially alternating relationship toprovide an even numbered blade array. One set of blades has a differentcharacteristic than the other set of blades to provide two differentresonant frequencies. For fixed stages, vanes have been mistuned byproviding different sets of vanes in adjacent quadrants of the array.

SUMMARY

In one exemplary embodiment, a stage for a gas turbine engine includes acircumferential airfoil array that provides a total airfoil count forthe stage and that includes first and second sets of airfoils. Theairfoil array has first, second, third and fourth arcuate regions. Thefirst and second arcuate regions are arranged opposite one another andthe third and fourth arcuate regions are arranged opposite one another.The first set of airfoils includes a different vibrational frequencythan the second set of airfoils. The first set of airfoils has firstprimary, first secondary and first tertiary airfoil groups. The secondset of airfoils has second primary, second secondary and second tertiaryairfoil groups. The first primary airfoil group and second primaryairfoil group are respectively arranged in the first and second arcuateregions. The first secondary airfoil group and second secondary airfoilgroup are arranged in the third arcuate region. The first tertiaryairfoil group and the second tertiary airfoil group are arranged in thefourth arcuate region. The first and second arcuate regions providegreater than 50% of the total airfoil count.

In a further embodiment of the above, the array is a stator vane stageand the airfoils are vanes.

In a further embodiment of any of the above, the stator vane stage isarranged in one of a compressor section and a turbine section of the gasturbine engine.

In a further embodiment of any of the above, the vanes are integratedwith an outer platform and are cantilevered.

In a further embodiment of any of the above, the first set of airfoilshas a different characteristic than the second set of airfoils toprovide the different vibrational frequency.

In a further embodiment of any of the above, the differentcharacteristic is at least one of an airfoil thickness, an airfoilshape, an airfoil spacing, a platform endwall shape, an airfoil materialand an airfoil weight.

In a further embodiment of any of the above, the differentcharacteristic is the airfoil spacing.

In a further embodiment of any of the above, the first and second setsof airfoils each have an airfoil spacing based upon a simulated stageairfoil count within +/−10 airfoils of the total airfoil count.

In a further embodiment of any of the above, the first set of airfoilshas an airfoil spacing based within +8 airfoils of the total airfoilcount. The second set of airfoils has an airfoil spacing based within −8airfoils of the total airfoil count.

In a further embodiment of any of the above, the first primary group,the first secondary group, the first tertiary airfoil group, the secondprimary group, the second secondary group and the second tertiaryairfoil group each include multiple airfoils.

In a further embodiment of any of the above, the multiple airfoils arearranged in clusters.

In a further embodiment of any of the above, the first secondary group,the first tertiary airfoil group, the second secondary group and thesecond tertiary airfoil group each include the same number of airfoilsas one another.

In a further embodiment of any of the above, the first primary group andthe second primary group each include a different number of airfoilsthan one another.

In a further embodiment of any of the above, the first primary group andthe second primary group each include the same number of airfoils as oneanother.

In a further embodiment of any of the above, the total airfoil count isprovided only by the first and second sets of airfoils.

In a further embodiment of any of the above, the airfoil array includesonly the first, second, third and fourth arcuate regions.

In a further embodiment of any of the above, a sum of the firstsecondary airfoil group and second secondary airfoil group arranged inthe third arcuate region provides less than 25% of the total airfoilcount. A sum of the first tertiary airfoil group and the second tertiaryairfoil group provides less than 25% of the total airfoil count.

In a further embodiment of any of the above, the first and secondarcuate regions provide greater than 75% of the total airfoil count.

In a further embodiment of any of the above, some of the airfoil groupscontain a third or fourth set of airfoils within them.

In another exemplary embodiment, a stage for a gas turbine engineincludes a circumferential airfoil array that provides a total airfoilcount for the stage and that includes first and second sets of airfoils.The airfoil array has first, second, third and fourth arcuate regions.The first and second arcuate regions are arranged opposite one another.The third and fourth arcuate regions are arranged opposite one another.The first set of airfoils includes a different vibrational frequencythan the second set of airfoils. The first set of airfoils has firstprimary, first secondary and first tertiary airfoil groups. The secondset of airfoils has second primary, second secondary and second tertiaryairfoil groups. The first primary airfoil group and second primaryairfoil group are respectively arranged in the first and second arcuateregions. The first secondary airfoil group and second secondary airfoilgroup are arranged in the third arcuate region. The first tertiaryairfoil group and the second tertiary airfoil group are arranged in thefourth arcuate region. The first and second arcuate regions providegreater than 50% of the total airfoil count. The first set of airfoilshas a different characteristic than the second set of airfoils toprovide the different vibrational frequency. The differentcharacteristic is an airfoil spacing where the first and second sets ofairfoils each have an airfoil spacing based upon a simulated stageairfoil count within +/−10 airfoils of the total airfoil count. Thefirst primary group, the first secondary group, the first tertiaryairfoil group, the second primary group, the second secondary group andthe second tertiary airfoil group each include multiple airfoils. Thefirst secondary group, the first tertiary airfoil group, the secondsecondary group and the second tertiary airfoil group each include thesame number of airfoils as one another.

In a further embodiment of the above, the array is a stator vane stageand the airfoils are vanes. The stator vane stage is arranged in one ofa compressor section and a turbine section of the gas turbine engine.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure can be further understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 schematically illustrates a gas turbine engine embodiment.

FIG. 2A is a schematic view through an engine section including a fixedstage and a rotating stage.

FIG. 2B illustrates airfoil clusters within a stage.

FIG. 3 is a perspective view of a stage having first and second airfoilsarranged in circumferentially alternating relationships with oneanother.

FIG. 4 is another example arrangement of airfoils.

The embodiments, examples and alternatives of the preceding paragraphs,the claims, or the following description and drawings, including any oftheir various aspects or respective individual features, may be takenindependently or in any combination. Features described in connectionwith one embodiment are applicable to all embodiments, unless suchfeatures are incompatible.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates a gas turbine engine 20. The gasturbine engine 20 is disclosed herein as a two-spool turbofan thatgenerally incorporates a fan section 22, a compressor section 24, acombustor section 26 and a turbine section 28. Alternative engines mightinclude an augmenter section (not shown) among other systems orfeatures. The fan section 22 drives air along a bypass flow path B in abypass duct defined within a nacelle 15, while the compressor section 24drives air along a core flow path C for compression and communicationinto the combustor section 26 then expansion through the turbine section28. Although depicted as a two-spool turbofan gas turbine engine in thedisclosed non-limiting embodiment, it should be understood that theconcepts described herein are not limited to use with two-spoolturbofans as the teachings may be applied to other types of turbineengines including three-spool architectures.

The exemplary engine 20 generally includes a low speed spool 30 and ahigh speed spool 32 mounted for rotation about an engine centrallongitudinal axis X relative to an engine static structure 36 viaseveral bearing systems 38. It should be understood that various bearingsystems 38 at various locations may alternatively or additionally beprovided, and the location of bearing systems 38 may be varied asappropriate to the application.

The low speed spool 30 generally includes an inner shaft 40 thatinterconnects a fan 42, a first (or low) pressure compressor 44 and afirst (or low) pressure turbine 46. The inner shaft 40 is connected tothe fan 42 through a speed change mechanism, which in exemplary gasturbine engine 20 is illustrated as a geared architecture 48 to drivethe fan 42 at a lower speed than the low speed spool 30. The high speedspool 32 includes an outer shaft 50 that interconnects a second (orhigh) pressure compressor 52 and a second (or high) pressure turbine 54.A combustor 56 is arranged in exemplary gas turbine 20 between the highpressure compressor 52 and the high pressure turbine 54. A mid-turbineframe 57 of the engine static structure 36 is arranged generally betweenthe high pressure turbine 54 and the low pressure turbine 46. Themid-turbine frame 57 further supports bearing systems 38 in the turbinesection 28. The inner shaft 40 and the outer shaft 50 are concentric androtate via bearing systems 38 about the engine central longitudinal axisX which is collinear with their longitudinal axes.

The core airflow is compressed by the low pressure compressor 44 thenthe high pressure compressor 52, mixed and burned with fuel in thecombustor 56, then expanded over the high pressure turbine 54 and lowpressure turbine 46. The mid-turbine frame 57 includes airfoils 59 whichare in the core airflow path C. The turbines 46, 54 rotationally drivethe respective low speed spool 30 and high speed spool 32 in response tothe expansion. It will be appreciated that each of the positions of thefan section 22, compressor section 24, combustor section 26, turbinesection 28, and fan drive gear system 48 may be varied. For example,gear system 48 may be located aft of combustor section 26 or even aft ofturbine section 28, and fan section 22 may be positioned forward or aftof the location of gear system 48.

The engine 20 in one example is a high-bypass geared aircraft engine. Ina further example, the engine 20 bypass ratio is greater than about six(6), with an example embodiment being greater than about ten (10), thegeared architecture 48 is an epicyclic gear train, such as a planetarygear system or other gear system, with a gear reduction ratio of greaterthan about 2.3 and the low pressure turbine 46 has a pressure ratio thatis greater than about five. In one disclosed embodiment, the engine 20bypass ratio is greater than about ten (10:1), the fan diameter issignificantly larger than that of the low pressure compressor 44, andthe low pressure turbine 46 has a pressure ratio that is greater thanabout five (5:1). Low pressure turbine 46 pressure ratio is pressuremeasured prior to inlet of low pressure turbine 46 as related to thepressure at the outlet of the low pressure turbine 46 prior to anexhaust nozzle. The geared architecture 48 may be an epicycle geartrain, such as a planetary gear system or other gear system, with a gearreduction ratio of greater than about 2.3:1. It should be understood,however, that the above parameters are only exemplary of one embodimentof a geared architecture engine and that the present invention isapplicable to other gas turbine engines including direct driveturbofans.

A significant amount of thrust is provided by the bypass flow B due tothe high bypass ratio. The fan section 22 of the engine 20 is designedfor a particular flight condition—typically cruise at about 0.8 Mach andabout 35,000 feet. The flight condition of 0.8 Mach and 35,000 ft, withthe engine at its best fuel consumption—also known as “bucket cruiseThrust Specific Fuel Consumption (‘TSFC’)”—is the industry standardparameter of lbm of fuel being burned divided by lbf of thrust theengine produces at that minimum point. “Low fan pressure ratio” is thepressure ratio across the fan blade alone, without a Fan Exit Guide Vane(“FEGV”) system. The low fan pressure ratio as disclosed hereinaccording to one non-limiting embodiment is less than about 1.45. “Lowcorrected fan tip speed” is the actual fan tip speed in ft/sec dividedby an industry standard temperature correction of [(Tram ° R)/(518.7°R)]^(0.5). The “Low corrected fan tip speed” as disclosed hereinaccording to one non-limiting embodiment is less than about 1150ft/second.

Referring to FIG. 2A, a portion of an engine section is shown, forexample, a turbine section. It should be understood, however, thatdisclosed section also may be provided in a compressor section.

The section includes a fixed stage 60 that provides a circumferentialarray of vanes 64 arranged axially adjacent to a rotating stage 62. Inthe example, the vane 64 includes an outer diameter portion 68 havinghooks 66 that support the array of vanes 64 with respect to a casestructure 74. An airfoil 70 is integral with and extends radially from aplatform of the outer diameter portion 68. In the examples that areillustrated, the vanes 64 are of the cantilevered type in which an innerdiameter portion 72 of the airfoil 70 is unsupported. It should beunderstood that the disclosed vane arrangement could be used for vanestructures having a platform at the inner diameter portion of theairfoil. The array of stator vanes may be provided as singlets,doublets, a full ring, ring halves or other multiples, as shown in FIG.2B.

Although the example stage is discussed in terms of stator vanes, thedisclosed mistuning configuration can be used for other arrays ofairfoils, such as blades in a rotating stage. The circumferentialairfoil array 80 provides a total airfoil count for the stage and thatincludes first and second sets of airfoils “A” and “B,” as shown in FIG.3. In the example, the first set of airfoils “A” has first primary,first secondary and first tertiary airfoil groups A1, A2, A3. The secondset of airfoils “B” has second primary, second secondary and secondtertiary airfoil groups B1, B2, B3. The terms “first,” “second,”“primary,” “secondary” and “tertiary” are not intended to connoteimportance or priority, but are used for identification purposes only.

The first set of airfoils “A” has a different characteristic than thesecond set of airfoils “B” to provide a different vibrational frequency.The different characteristic is at least one of an airfoil thickness, anairfoil shape, an airfoil spacing, a platform endwall shape, an airfoilmaterial and an airfoil weight. In the example, the differentcharacteristic is the airfoil spacing.

In one example shown in Table 1, the stage has a total airfoil count of42. The first and second sets of airfoils “A,” “B” each have an airfoilspacing based upon a simulated stage airfoil count within +/−10 airfoilsof the total airfoil count, in the example, 42. For example, the firstset of airfoils “A” has an airfoil spacing based within +8 airfoils ofthe total airfoil count, for example, 46.70. The second set of airfoils“B” has an airfoil spacing based within −8 airfoils of the total airfoilcount, for example, 38.16. As can be appreciated from the examples, thesimulated airfoil count may or may not be an integer. So, within thegroupings of the first set of airfoils “A,” the vanes are more tightlypacked together than in the grouping of the second set of airfoils “B,”which provides different airfoil spacing and mistuning within the stage.

The airfoil array 80 has first, second, third and fourth arcuateregions, 82, 84, 86, 88, respectively. The first and second arcuateregions 82, 84 are arranged opposite one another, and the third andfourth arcuate regions 86, 88 are arranged opposite one another.

The first primary group A1, the first secondary group A2, the firsttertiary airfoil group A3, the second primary group B1, the secondsecondary group B2 and the second tertiary airfoil group B3 each includemultiple airfoils. The multiple airfoils are arranged in clusters. Thefirst primary airfoil group A1 and second primary airfoil group B1 arerespectively arranged in the first and second arcuate regions 82, 84.The first secondary airfoil group A2 and second secondary airfoil groupB2 are arranged in the third arcuate region 86. The first tertiaryairfoil group A3 and the second tertiary airfoil group B3 are arrangedin the fourth arcuate region 88.

The first and second arcuate regions 82, 84 and the first and secondairfoils within those regions provide greater than 50% of the totalairfoil count. In one example, the first and second arcuate regions andits airfoils provide greater than 75% of the total airfoil count. A sumof the first secondary airfoil group A2 and the second secondary airfoilgroup B2 arranged in the third arcuate region 86 provides less than 25%of the total airfoil count. Similarly, a sum of the first tertiaryairfoil group A3 and the second tertiary airfoil group B3 provides lessthan 25% of the total airfoil count. Several example stages are shown inTable 1 below.

TABLE 1 Example 1 Example 2 Example 3 # of airfoils 42 51 48 Spacing forA# of 46.70 56.85 54.12 airfoils Spacing for B# of 38.16 46.73 44.41airfoils Airfoil count A1 15 18 14 Airfoil count B1 15 21 21 Airfoilcount A2 3 3 3 Airfoil count B2 3 3 4 Airfoil count A3 3 3 3 Airfoilcount B3 3 3 3

As can be seen in table above, the number of airfoils between the groupsmay be the same or different.

In the examples, the total airfoil count is provided only by the firstand second sets of airfoils “A,” “B,” and the airfoil array 80 includesonly the first, second, third and fourth arcuate regions 82, 84, 86, 88.More than two different airfoils may be used and more than four arcuateregions may be provided.

In another example shown in FIG. 4, the airfoil array 180 includesfirst, second, third and fourth arcuate regions 182, 184, 186, 188. Someof the first set of vanes C1 are arranged in the first arcuate region182, and some of the second set of vanes D1 are arranged in the secondarcuate region 184. Instead of pairs of vane clusters in the third andfourth arcuate regions 186, 188, additional clusters are provided (e.g.,C2, D2, C3, D3 in the third arcuate region 186; C4, D4, C5, D5 in thefourth arcuate region 188).

The first and second sets of airfoils “A,” “B” have different vibrationfrequencies than one another to mistune the array of vanes and reducethe structural and aerodynamic coupling between adjacent vanes. As aresult, the airfoil resonant vibration response, the vibration responseafter engine compressor stall from aerodynamic separation inducedvibration, and the airfoil aero-elastic flutter vibration response allmay be reduced. An array of non-mistuned airfoils, because they all areof the same shape and spacing, reinforce a single vibratory frequency.Mistuning an array disperses vibration reinforcement among multiplefrequencies; each at a reduced amount. For instance, Table 2 shows thatthe array from Example 1 in Table 1 disperses reinforcement amongmultiple frequencies. So, in a stage having 42 equally spaced airfoils,a multiple of engine RPM coinciding with this number of airfoils, i.e.,42, would tend to excite an adjacent blade to a high degree. Thedisclosed mistuning arrangement results in a significant vibrationreduction at this engine RPM multiple, for example, up to 35%. This ismuch greater than current mistuning method.

TABLE 2 Multiple of engine RPM 37 38 39 40 41 42 43 44 45 46 47 48 49Max 0.30 0.23 0.29 0.35 0.13 0.35 0.19 0.25 0.29 0.20 0.34 0.35 0.06vibration reinforcement

It should also be understood that although a particular componentarrangement is disclosed in the illustrated embodiment, otherarrangements will benefit herefrom. Although particular step sequencesare shown, described, and claimed, it should be understood that stepsmay be performed in any order, separated or combined unless otherwiseindicated and will still benefit from the present invention.

Although the different examples have specific components shown in theillustrations, embodiments of this invention are not limited to thoseparticular combinations. It is possible to use some of the components orfeatures from one of the examples in combination with features orcomponents from another one of the examples.

Although an example embodiment has been disclosed, a worker of ordinaryskill in this art would recognize that certain modifications would comewithin the scope of the claims. For that reason, the following claimsshould be studied to determine their true scope and content.

What is claimed is:
 1. A stage for a gas turbine engine comprising: acircumferential airfoil array providing a total airfoil count for thestage and that includes first and second sets of airfoils, the airfoilarray has first, second, third and fourth arcuate regions, the first andsecond arcuate regions arranged opposite one another, and the third andfourth arcuate regions arranged opposite one another, the first set ofairfoils includes a different vibrational frequency than the second setof airfoils, the first set of airfoils has first primary, firstsecondary and first tertiary airfoil groups, the second set of airfoilshas second primary, second secondary and second tertiary airfoil groups,the first primary airfoil group and second primary airfoil grouprespectively arranged in the first and second arcuate regions, the firstsecondary airfoil group and second secondary airfoil group arranged inthe third arcuate region, and the first tertiary airfoil group and thesecond tertiary airfoil group arranged in the fourth arcuate region, thefirst and second arcuate regions provide greater than 50% of the totalairfoil count.
 2. The stage according to claim 1, wherein the array is astator vane stage, and the airfoils are vanes.
 3. The stage according toclaim 2, wherein the stator vane stage is arranged in one of acompressor section and a turbine section of the gas turbine engine. 4.The stage according to claim 2, wherein the vanes are integrated with anouter platform and are cantilevered.
 5. The stage according to claim 1,wherein the first set of airfoils has a different characteristic thanthe second set of airfoils to provide the different vibrationalfrequency.
 6. The stage according to claim 5, wherein the differentcharacteristic is at least one of an airfoil thickness, an airfoilshape, an airfoil spacing, a platform endwall shape, an airfoil materialand an airfoil weight.
 7. The stage according to claim 6, wherein thedifferent characteristic is the airfoil spacing.
 8. The stage accordingto claim 7, wherein the first and second sets of airfoils each have anairfoil spacing based upon a simulated stage airfoil count within +/−10airfoils of the total airfoil count.
 9. The stage according to claim 8,wherein the first set of airfoils has an airfoil spacing based within +8airfoils of the total airfoil count, and the second set of airfoils hasan airfoil spacing based within −8 airfoils of the total airfoil count.10. The stage according to claim 1, wherein the first primary group, thefirst secondary group, the first tertiary airfoil group, the secondprimary group, the second secondary group and the second tertiaryairfoil group each include multiple airfoils.
 11. The stage according toclaim 10, wherein the multiple airfoils are arranged in clusters. 12.The stage according to claim 1, wherein the first secondary group, thefirst tertiary airfoil group, the second secondary group and the secondtertiary airfoil group each include the same number of airfoils as oneanother.
 13. The stage according to claim 1, wherein the first primarygroup and the second primary group each include a different number ofairfoils than one another.
 14. The stage according to claim 1, whereinthe first primary group and the second primary group each include thesame number of airfoils as one another.
 15. The stage according to claim1, wherein the total airfoil count is provided only by the first andsecond sets of airfoils.
 16. The stage according to claim 1, wherein theairfoil array includes only the first, second, third and fourth arcuateregions.
 17. The stage according to claim 1, wherein a sum of the firstsecondary airfoil group and second secondary airfoil group arranged inthe third arcuate region provides less than 25% of the total airfoilcount, and a sum of the first tertiary airfoil group and the secondtertiary airfoil group provides less than 25% of the total airfoilcount.
 18. The stage according to claim 1, wherein the first and secondarcuate regions provide greater than 75% of the total airfoil count. 19.The stage according to claim 1, where some of the airfoil groups containa third or fourth set of airfoils within them.
 20. A stage for a gasturbine engine comprising: a circumferential airfoil array providing atotal airfoil count for the stage and that includes first and secondsets of airfoils, the airfoil array has first, second, third and fourtharcuate regions, the first and second arcuate regions arranged oppositeone another, and the third and fourth arcuate regions arranged oppositeone another, the first set of airfoils includes a different vibrationalfrequency than the second set of airfoils, the first set of airfoils hasfirst primary, first secondary and first tertiary airfoil groups, thesecond set of airfoils has second primary, second secondary and secondtertiary airfoil groups, the first primary airfoil group and secondprimary airfoil group respectively arranged in the first and secondarcuate regions, the first secondary airfoil group and second secondaryairfoil group arranged in the third arcuate region, and the firsttertiary airfoil group and the second tertiary airfoil group arranged inthe fourth arcuate region, the first and second arcuate regions providegreater than 50% of the total airfoil count; wherein the first set ofairfoils has a different characteristic than the second set of airfoilsto provide the different vibrational frequency, the differentcharacteristic is an airfoil spacing; wherein the first and second setsof airfoils each have an airfoil spacing based upon a simulated stageairfoil count within +/−10 airfoils of the total airfoil count; whereinthe first primary group, the first secondary group, the first tertiaryairfoil group, the second primary group, the second secondary group andthe second tertiary airfoil group each include multiple airfoils; andwherein the first secondary group, the first tertiary airfoil group, thesecond secondary group and the second tertiary airfoil group eachinclude the same number of airfoils as one another.
 21. The stageaccording to claim 20, wherein the array is a stator vane stage, and theairfoils are vanes, the stator vane stage is arranged in one of acompressor section and a turbine section of the gas turbine engine.